The present invention relates to a reinforced membrane and in particular to a recyclable reinforced membrane including two propylene-ethylene-copolymer (thermoplastic olefin or xe2x80x9cTPOxe2x80x9d) sheets bonded to each other and to a polypropylene reinforcing mesh intermediate the propylene-ethylene-copolymer sheets. While the reinforced membrane of the present invention can be used for other applications, the reinforced membrane of the present invention is particularly well suited for use as a membrane in a single ply roofing system.
Single ply roofing membrane systems are commonly used as the roofing systems for low sloping roofs, especially in industrial and commercial applications. Typically, these single ply roofing membrane systems utilize roofing membranes which each include two propylene-ethylene-copolymer sheets bonded to each other and to a woven polyester reinforcing mesh or scrim located intermediate the propylene-ethylene-copolymer sheets. The propylene-ethylene-copolymer sheets provide the reinforced roofing membrane with good flexibility (including low temperature flexibility), good heat aging resistance, and good UV weathering characteristics. In addition the propylene-ethylene-copolymer sheets enable the roofing membranes in a roofing system to be hot air welded together. The woven polyester mesh or scrim in the roofing membrane provides the reinforced membrane with good tensile strength, puncture resistance and tear resistance.
While membranes using woven polyester meshes to reinforce the membranes perform satisfactorily, the use of woven polyester meshes in single ply roofing membranes has several drawbacks. A first problem associated with the use of woven polyester meshes in roofing membranes is the hydrophilic nature of such polyester meshes. Due to the hydrophilic nature of these polyester meshes, in use, roofing membranes made with polyester meshes will wick water into the roofing membranes along unsealed edges of the membranes and cause a deterioration in the performance of the roofing system. In addition, due to the incompatibility of these polyester meshes and the propylene-ethylene-copolymer sheets, another problem associated with the use of woven polyester meshes in roofing membranes made with propylene-ethylene-copolymer sheets is the inability to recycle scrap membrane, e.g. trim, back into the process producing the roofing membrane or to recycle the roofing membrane after use.
The following patents are representative of various roofing systems in the prior art. U.S. Pat. No. 3,663,350, issued May 16, 1972, discloses a roof deck laminate which includes a nylon, Dacron or polyester scrim between two polyvinyl chloride layers. U.S. Pat. No. 4,636,414, issued Jan. 13, 1987 discloses a bituminous roofing membrane which includes bituminous layers laminated to a fibrous sheet which may be made of polypropylene and a synthetic resin sheet. U.S. Pat. No. 5,260,111, issued Nov. 9, 1993, discloses a roofing membrane made of two rubber sheets and an intermediate sheet of thermoplastic film. U.S. Pat. No. 5,687,517, issued Nov. 18, 1997, discloses a roofing underlayment including at least two multi-layer plastic films.
The single ply membrane of the present invention may reduce the wicking problem associated with polyester scrim reinforced membranes and can be recycled both during the production process, if the membrane is out of specification, and after the membrane""s useful service life in the field. While the membrane of the present invention can be used for other applications, the membrane of the present invention is especially well suited for use as a membrane in a single ply roofing membrane system.
The membrane of the present invention includes a pair of propylene-ethylene-copolymer (TPO) sheets and a polypropylene reinforcing mesh intermediate and bonded to the propylene-ethylene-copolymer sheets. Preferably, the propylene-ethylene-copolymer of the sheets is polymerized from a polypropylene and ethylene-monomer blend made up of about 30% to about 70% by weight polypropylene and about 30% to about 70% by weight ethylene-monomer. Preferably, the ethylene-monomer used in the blend results in an ethylene-propylene-rubber; an ethylene-propylene-monomer or an ethylene-propylene-diene-monomer (these are thermoplastic olefins which are referred to as xe2x80x9cTPOsxe2x80x9d).
Since the polypropylene mesh is hydrophobic rather than hydrophilic like the polyester mesh, the wicking of water into the membrane along raw edges of the membrane while the membrane is in service should be reduced thereby enhancing the long term performance of the membrane. The chemical compatibility of the polypropylene mesh with the propylene-ethylene-copolymer sheets enables out of specification scrap produced during the manufacture of the membrane to be ground or chopped and recycled back into the process. After the membrane""s useful service life, the chemical compatibility of the polypropylene mesh with the propylene-ethylene-copolymer sheets further enables the entire membrane to be recycled into another roofing product, such as atactic polypropylene (xe2x80x9cAPP-modified bitumenxe2x80x9d) roofing systems. In addition, the chemical compatibility of the polypropylene mesh and the propylene-ethylene-copolymer sheets promotes better bonding between the mesh and the sheets and provides the membrane with greater interlaminar strength.